Spherical halogen geiger tube

ABSTRACT

A nondirectional halogen quenched Geiger tube having concentrically arranged spherical anode and cathode, the space between the electrodes being filled with a gaseous mixture of neon, argon and bromine, which electrical connections provided to the two electrodes.

United States Patent Panther et a1.

SPHERICAL HALOGEN GEIGER TUBE Richard H. Panther; Charles Ralph Purser, both of Ottawa, Ontario, Canada Her Majesty the Queen in right of Canada as represented by the Minister of National Defence of Her Majestys Canadian Government Filed: Nov. 4, 1968 Appl. No.: 773,095

Inventors:

Assignee:

[30] Foreign Application Priority Data Dec. 19, 1967 Canada ..007,990

us. c1 ..313/93, 313/217, 313/226, 313/247 1111.01 ..H01j 39/26, 1101 17/06, H013 61/16 Field Of Search .313/93, 112, 291; 250/836,

[56] References Cited UNITED STATES PATENTS 1,985,086 12/1934 Geffckeneta1 313/29 l x 1 Feh.29,1972

2,858,465 11/1958 Ludeman ..3l3/93 2,963,589 12/1960 Neher et al. ..313/93 X 3,366,790 1/1968 Zagorites et al.. 1 3/93 X 3,372,279 3/1968 Engh et al .l .3! 3/93 X FOREIGN PATENTS OR APPLICATIONS 69,937 4/1915 Austria ..250/83.6

OTHER PUBLICATIONS Spherical Proportional Counter" H. Agnew, US. Patent Office Scientific Library, June 1949, cover page, pages 1, 2 and 3 and FIG. 1.

Primary ExaminerRobert Segal Attorney-Graham & Baker [57] ABSTRACT A nondirectional halogen quenched Geiger tube having concentrically arranged spherical anode and cathode, the space between the electrodes being filled with a gaseous mixture of neon, argon and bromine, which electrical connections provided to the two electrodes.

2 Claims, 2 Drawing Figures SPHERICAL HALOGEN GEIGER TUBE BRIEF SUMMARY OF THE INVENTION The present invention relates to an improved Geiger counter tube and in particular to a spherical, halogen quenched, Geiger tube having greatly improved properties over known Geiger counters.

BACKGROUND OF THE INVENTION Up to the present time Geiger tubes have been of generally cylindrical configuration. These tubes have suffered from end effects" which result in weakening of the electrical field toward the end of the cathode. Such tubes have given a nonuniform response depending upon the position of the source of radiation in relation to the tube. In known Geiger tubes, the cathode is a right cylinder and any energy dependent filter associated with the tube is generally coaxial with the cathode. Accordingly, the radiation from the source is modified by the filter according to the angle of the source relevant to the tube. In the past attempts have been made to overcome this defect by providing a very complex filter of many differing wall thicknesses. This complex filter does improve the operation of the tube but the overall result obtained is still considerably variable and, of course, such a complex filter is expensive and often difficult to mount.

DESCRIPTION OF THE PRIOR ART In U.S. Pat. No. 2,858,465 there is shown in FIG. 2 a multiple cathode Geiger tube in which spherical cathodes are mounted concentrically and which is provided with a series of radially extending wire anodes which project through the cathodes at spaced intervals and are insulated from the cathodes by insulating beads. Numerous problems are encountered in the construction of such a counter, for example, it is almost impossible accurately to center the individual anode wires in the clearance holes in the many cathode shells, thus, it would be almost impossible to maintain a constant voltage gradient throughout the counter. Also, the many insulating anchor points for the anode wires at their terminal points in the outer cathode shell pose a sealing problem not easy to resolve in an organic tube and virtually impossible in a tube containing a halogen.

DESCRIPTION OF THE INVENTION The applicant's design eliminates these difiiculties by maintaining a constant cathode to anode spacing within the active volume without the impractical complex of wires and thus achieves a substantially constant voltage gradient at all positions between the cathode and anode. Maintenance of a constant voltage gradient at all points between the cathode and anode is necessary to achieve the uniform plateau slope for ionization created by radiation from random directions.

The Geiger tube constructed in accordance with the teachings of the present invention is substantially free from directional effects and may readily be provided with a simple filter for example, by forming a coating directly on the outside of the Geiger tube.

The improved operation of the Geiger tube of the present invention provides numerous advantages in the detection of gamma and beta radiation, for example, in the measurement of nuclear fallout.

In accordance with the present invention, a spherical halogen quenched Geiger tube is provided which is so proportioned as to maintain a constant wall thickness and preserve a consistent voltage gradient throughout the active volume which thus preserves the Geiger characteristic of the tube and avoids the tube becoming a proportional counter. It will be appreciated that the spherical form of the Geiger tube of the invention enables a filter of the same form to envelope the tube and be of a consistent thickness. Regardless of the source angle relative to the tube, for any given energy, the response will be consistent and a much more accurate filter may be made. The area presented to the source is constant within the active zone of the tube.

In accordance with the invention the Geiger tube consists of two concentric spheres, an outer sphere which is the cathode and an inner sphere which is the anode. The radial distance between their surfaces preferably varies by no more than approximately one one-hundredth of the spacing between these surfaces. The active volume of the Geiger tube is thus contained between the spherical cathode and the spherical anode. This active volume is the volume which the entire surface arcs of the cathode subtends on the surface area of the anode. Preferably in accordance with the invention, the cathode area may be of the order of nine times the anode area through other ratios are also suitable.

In accordance with a preferred embodiment of the invention the cathode is constructed of thin bore-silicate or Pyrex glass on the inner surface of which a metal layer has been deposited by electroless nickel plating as described in U.S. Pat. application, Ser. No. 744,637 filed July 15, l968 the inventors being Arthur W. L. Bridge, Keith W. Rodie and Arthur L. Bree. Preferably, this coating is uniform and of even thickness of approximately 0.00] inch. In the alternative, the cathode may be formed as a free standing electroform without the need of a supporting glass sphere. As constructed, the cathode is provided with a circular aperture through which the anode is admitted and which also provides space for a glass base to support the anode and for carrying a pumping tube through which the Geiger tube may be filled. The aperture formed in the cathode should be of such a diameter that the distance between any point on the cathode at the aperture and the nearest point on the anode support is equal to or greater than the radial distance between the anode and the cathode. Preferably the aperture diameter should not excess 0.4 of the cathode diameter.

The anode used in the Geiger tube of the present invention may be a thin walled sphere of a material similar to the cathode, a solid sphere, a wire mesh sphere, or a glass or a plastic sphere upon the outer surface of which metal has been deposited for example, electrolytically, the anode being mounted to the glass base so that when the subassembly is fitted into a suitable jig designed to hold the cathode for the purpose of joining the two component parts together, the geometric relationship of the cathode and anode and the anode support wire is maintained.

The gas filling used in the Geiger tube of the present invention is a conventional halogen quenched Geiger tube filling consisting of a mixture of neon, argon and bromine in the proportions for example of 0.1 percent Argon/Bromine in Neon at a pressure of for example 10 cm. Hg.

When constructed in accordance with the foregoing limitations, the Geiger tube of the invention will have a true Geiger platform of uniform slope since the voltage gradient within the Geiger tube remains constant. No undesirable end effects will be apparent and the efficiency of the tube is higher than with a known cylindrical Geiger tube since the electrical field is uniform throughout the entire active volume of the tube. Such a tube shows consistent directional response to energies between Kev. and 5 Mev. regardless of source angle relative to the active volume of the tube. Thus it is possible to deposit a suitable filter of constant thickness either on the inside of the glass cathode sphere prior to deposition of the cathode proper or on the outside of the glass sphere or on a free standing cathode structure. In this way the filter is an integral part of the tube instead of a separate item as with known cylindrical Geiger tubes. It is also within the scope of the present invention to provide a cathode of a material suitably chosen so that it functions as both cathode and filter to meet the requirements of the specific application of the Geiger tube.

It will be appreciated that the design of the Geiger tube in accordance with the present invention is considerably more rugged than the previous cylindrical designs and it is thus better able to withstand mechanical accelerations and abuse which occurs in portable applications of the Geiger tube.

The admittance of medium energy beta particles can be obtained with a Geiger tube of the present invention by the appropriate choice of the thickness of the glass sphere supporting the cathode since by its configuration the tube will withstand greater atmospheric pressure variations than are possible with the known end-window type of Geiger tube. For low-energy beta particles the cathode could be comprised of a glass sphere 0.001 inches thick with a metal cathode electrolytically deposited on the inside surface to a mardrnum thickness of 0.0005 inches and the whole protected by an envelope of wire mesh or a thicker plastic sphere with an equally thin metal deposited on its inside surface.

The Geiger tube of the present invention will permit greater overall accuracy of the monitoring of fallout fields due to the tubes less directional response within its active volume. The method of construction of the tube is simple and inexpensive and well within the scope of the average vacuum tube manufacturers facilities. The tube of the present invention is relatively insensitive to voltage changes within its plateau thus it can be operated efiiciently from a simple inexpensive power supply.

BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings which illustrate the construc tion and use of an embodiment of the present invention:

FIG. 1 is a longitudinal cross section of a Geiger tube constructed in accordance with the present invention and,

FIG. 2 is an electrical schematic diagram showing the use of a Geiger tube constructed in accordance with the applicant's invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, there is shown a Geiger tube constructed in accordance with one embodiment of the applicants invention. This Geiger tube consists of an outer spherical cathode form 11 on the inner surface of which the cathode 12 is adhered. Within the volume of the cathode there is provided an anode form 13 on the exterior of which the anode 14 is similarly adhered. The space between the anode and cathode is filled with a conventional Geiger mixture of neon,

with 0.1 percent argon and bromine at a pressure of 10 cm. Hg for example. The anode form 13 is mounted on an anode support tube 15 preferably formed of a metal alloy sold under the trademark "KOVAR which support 15 extends through a glass-to-metal seal 16 for making connection with the anode l4 and external circuits. Similarly, the metallic cathode which is preferably an electroless plated nickel film is connected to external circuits by a cathode connection 17 also formed of the metal alloy sold under the trademark KOVAR." A filler tube 18 is provided in the structure through which the neon, argon, bromine gas mixture may be introduced into the Geiger tube after the tube has been constructed.

Preferably, the cathode form 11 is made of boro-silicate or Pyrex glass which is bonded during construction to the glass to metal seal 16 to form the completed Geiger tube. Similarly, the anode form 13 may also conveniently be formed of borosilicate glass on which the anode 14 has been deposited by an electroless nickel coating process such as disclosed in copending application Ser. No. 744,637 as aforesaid.

FIG. 2 illustrates an electrical schematic of the Geiger tube of FIG. 1 when connected in an electric circuit for measuring the properties of the tube. The tube 10 has its cathode 12 connected to an electrical scaler for counting impulses for the Geiger tube, the cathode being grounded through a resistor 20 which may, for example, be 8.2 kfl. The anode 14 is connected to a source of high voltage 21 via the 2.2 m0 resistor 22. The Geiger tube is placed in the field to be measured and the number of counts obtained at the scaler 23 is recorded.

In the following table the properties of two separately dimensioned Geiger tubes in accordance with the present invention are recorded:

Gamma range background to I00 milliroentgens per hour in Geiger background to 40 rnilliroentgens per hour in Geiger A 7 mode mode C ountsat I00 I 7 V V V 'i milliroentgens per hr. l 7,QQtl Counts at 40 miliiroentgens per hr. l90.000

Directional response uniform within active volume The above results were obtained with the tubes constructed as shown in FIG. 1 filled with a neon, argon, bromine mixture and connected in a circuit as shown in FIG. 2. The data were determined in a cobalt 60 field. The tube is not light semitive.

We claim:

I. A nondirectional halogen quenched Geiger tube comprising a substantially spherical cathode, said cathode comprising a nickel film formed on the interior of a substantially spherical insulating cathode substrate and having an aperture therein, a substantially spherical anode, said anode comprising a nickel film formed on the exterior of a substantially spherical insulating anode substrate, said cathode having a surface area approximately nine times the area of said anode, means extending through said aperture for supporting said anode concentrically within said anode substrate being mounted on said means for supporting said anode concentrically within said cathode, means for sealing said anode support means to said cathode substrate, said cathode, said aperture being of such a size that the distance between any point on said cathode at said aperture and the nearest point on said anode support means is equal to or greater than the radial distance between said anode and said cathode, the space between said cathode and said anode being sealed and filled with a gaseous mixture of neon and a relatively small percentage of a mixture of argon and bromine to a pressure of approximately 10 centimeters of mercury, first terminal means electrically connected with said cathode, and second terminal means electrically connected with said anode.

2. A Geiger tube as claimed in claim 1 wherein said gaseous mixture comprises 0.1 percent of a mixture of argon and bromine with the rest being essentially neon. 

1. A nondirectional halogen quenched Geiger tube comprising a substantially spherical cathode, said cathode comprising a nickel film formed on the interior of a substantially spherical insulating cathode substrate and having an aperture therein, a substantially spherical anode, said anode comprising a nickel film formed on the exterior of a substantially spherical insulating anode substrate, said cathode having a surface area approximately nine times the area of said anode, means extending through said aperture for supporting said anode concentrically within said anode substrate being mounted on said means for supporting said anode concentrically within said cathode, means for sealing said anode support means to said cathode substrate, said cathode, said aperture being of such a size that the distance between any point on said cathode at said aperture and the nearest point on said anode support means is equal to or greater than the radial distance between said anode and said cathode, the space between said cathode and said anode being sealed and filled with a gaseous mixture of neon and a relatively small percentage of a mixture of argon and bromine to a pressure of approximately 10 centimeters of mercury, first terminal means electrically connected with said cathode, and second terminal means electrically connected with said anode.
 2. A Geiger tube as claimed in claim 1 wherein said gaseous mixture comprises 0.1 percent of a mixture of argon and bromine with the rest being essentially neon. 